Table 1.

Number of genes in the 27 representative genomes and number of symbiosis genes.

	all genes	nodulation	N-fixation	host benefit	rhizobial fitness
number of genes	29 671	65	55	10	21
proportion genes that are single-copy	0.86	0.54	0.51	0.40	0.43
median family size	2	8	27	19.5	18
proportion of genes in all genomes	0.04	0.17	0.40	0.50	0.24
prop. of genes found in one genome	0.48	0.05	0.07	0.10	0.05
median number of genomes	2	6	22	19	17
mean copies/genome	1.07	1.22	1.26	1.37	1.45
number of genes also found in
nodulation		—	0	2	0
N-fixation			—	4	2
host benefit				—	0